public class ThreadHelper {

    private TextView textView;

    public ThreadHelper(TextView textView) {
        this.textView = textView;
    }

    public void runOnAnotherThread() {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                textView.post(new Runnable() {
                    @Override
                    public void run() {
                        textView.setText("FirstText");
                    }
                });
            }
        });
        thread.start();
    }

    public void addText(final String text){
        textView.post(new Runnable() {
            @Override
            public void run() {
                textView.setText(textView.getText() + "\n" + text);
            }
        });
    }
}